(1)Field of the Invention
The invention relates generally to electrical switching apparatus and, mare particularly, to electrical switching apparatus, such as circuit breakers, having contact spring assemblies.The invention also relates to contact spring assemblies for circuit breaker movable contact assemblies.
(2) Background Information
Electrical switching apparatus, such as circuit breakers, provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits, abnormal voltage and other fault conditions. Typically, circuit breakers include an operating mechanism which opens electrical contact assemblies to interrupt the flow of current trough the conductors of an electrical system in response to such fault conditions.
Many low-voltage circuit breakers, for example, employ a molded housing having two parts, a first half or front part (e.g., a molded cover), and a second half or rear part (e.g., a molded base). The operating mechanism for such circuit breakers is often mounted to the front part of the housing, and typically includes an operating handle and/or button(s) which, at one end, is (are) accessible from the exterior of the molded housing and, at the other end, is (are) coupled to a pivotable pole shaft. Electrical contact assemblies, which are also disposed within the molded housing, generally comprise a conductor assembly including a movable contact assembly having a plurality of movable contacts, and a stationary contact assembly having a plurality of corresponding stationary contacts. The movable contact assembly is electrically connected to a generally rigid conductor of the conductor assembly by flexible conductors, commonly referred to as shunts. The movable contact assembly includes a plurality of movable contact arms or fingers, each carrying one of the movable contacts and being pivotably coupled to a contact arm carrier. The contact arm carrier is pivoted by a protrusion or arm on the pole shaft of the circuit breaker operating mechanism to move the movable contacts into and out of electrical contact with the corresponding stationary contacts of the stationary contact assembly. The contact arm carrier includes a contact spring assembly structured to bias the fingers of the movable contact assembly against the stationary contacts of the stationary contact assembly in order to provide and maintain contact pressure when the circuit breaker is closed, and to accommodate wear.
More specifically, some low-voltage power circuit breakers require contact pressure to be maintained during operation, in order to achieve the desired thermal and interruption performance. To provide such pressure, it has been known to employ contact spring assemblies which are coupled to the contact arm carrier and structured to bias the contact arms or fingers, and the movable contacts disposed thereon, toward the stationary contacts. See, e.g., U.S. Pat. Nos. 6,005,206 and 6,977,568, which are hereby incorporated herein by reference.
Among the disadvantages of such contact spring assemblies is that they are relatively complex in design, employing a relatively large number of springs (e.g., at least one set of eight or more springs), and comprising a unit which is separate from, and disposed beside (i.e., behind and/or adjacent to), the contact arm carrier. As a result, the contact spring assembly not only consumes valuable space within the circuit breaker housing, it is also relatively difficult to assemble. Moreover, the large size and inconvenient location of the contact spring assembly reduces the dimension within the circuit breaker housing which is available to accommodate the motion of the movable contact assembly during the various stages (e.g., opening; closing; tripping open in response to a fault condition) of its operation. It also adds mass, which decreases the opening velocity of the movable contact assembly, thus adversely affecting the circuit interruption performance of the circuit breaker. A still further disadvantage is the fact that contact pressure is not provided separately to each individual contact arm or finger of the movable contact assembly. Rather, the springs of known contact assemblies bias a common element (e.g., a cam element) which engages all of the fingers simultaneously.
It is desirable, therefore, to provide a contact spring assembly which provides accurate and consistent contact pressure to the individual fingers or contact arms of the movable contact assembly, and which allows independent contact arm movement while being tolerant of manufacturing variation, cost-effective to manufacture, compact in size, and relatively easy to assemble.
There is, therefore, room for improvement in contact spring assemblies for the movable contact assemblies of electrical switching apparatus such as, for example, low-voltage circuit breakers.